You could fix that just by applying some clear acrylic sealer (or clear nail polish) over it with an artist's paint brush.
You don't need to know the rest. Most people would intuitively feel that a clear coat over that scratch would hide it, but I'll explain WHY a clear coat will hide such a scratch.
The reason why is due to something called Fresnel's Law, which governs reflection of light from an interface. Fresnel's Law says that the percentage of light reflected off an interface is proportional to the difference in refractive indices divided by the sum of the refractive indices across that interface, all squared.
That is: fraction of light reflected = ((n1 - n2)/(n1+n2)) ^2
Where n1 and n2 are the refractive indices of the media on each side of the interface, respectively.
Since you have air (a gas) on one side of that scratch interface and Marmoleum (a solid) on the other, then the difference between the refractive indices are going to be large, and much of the incident light is going to be reflected from the rough surface of that scratch.
Rough surfaces are most commonly white in colour because the roughness of the surface scatters incident light, and your eye sees the resulting scattered light as the colour "white". If you scratch anything, it will be a WHITE scratch, or a WHITISH scratch.
The reason for scratches being white is that no material known to man is completely opaque, and every material allows light to penetrate into it SOME distance before it's all absorbed. The most opaque materials are metals. You can block more light with aluminum foil than you can with any other material of equal thickness. Still, even metal is not completely opaque. The Low-e coating on modern windows consists of silver atoms, about 70 atoms thick, and most of the incident light will pass completely through that silver film so that it takes some practice to even tell if the silver coating is even there. Thus, even the most opaque material known to man, allows light to pass through it some distance.
So, if you scratch a material, you create a rough surface that both reflects incident light, and refracts that incident light as it enters the material. Some of the light that enters the material is reflected back out to your eye by things inside the material. (This is why the red pigments inside red paint make the paint look red to your eye; the light reflects off red pigments inside an otherwise clear plastic film.) The reflecting and refracting of light that goes on at the scratch and immediately under it causes incident light to be scattered in different directions, causing it to be broken up into different frequencies (or colours) and your eye sees the mixture of different colours coming from the scratch as the colour "white". The result is that the scattered "white" light will add to the colour of the material itself to give you a scratch that looks whiter or lighter than the surrounding material. Scratch concrete or even glass, and you'll find it's a white scratch, and the reason is the same for all materials; scattered light looks white to the eye.
Let's put some numbers into Fresnel's Law for this scratch. The refractive index of air is close enough to 1.00 to be called 1.00. Let's presume the refractive index of marmoleum is 1.8 and that of clear nail polish is 1.5, say. I pick 1.5 for clear nail polish because the refractive index of glass is about 1.5, and it's a solid.
Without any nail polish over the scratch, then the fraction of incident light reflected from the scratch surface is:
fraction = ((1.8 - 1)/(1.8 + 1))^2 or (0.8/2.8)^2 or 8.2 percent.
If we now paint over that scratch with clear nail polish, there are now TWO interfaces; the air/nail_polish interface and the nail_polish/marmoleum interface. The amount of light reflected off the relatively smooth air/nail_polish interface is:
fraction = ((1.5 - 1)/ 1.5+1))^2 or (0.5/2.5)^2 or 8.0 percent
wheras the amount of light reflected from the relatively rough nail_polish/marmoleum interface is now:
fraction = ((1.8-1.5)/(1.8+1.5))^2 or (0.3/3.3)^2 or 0.8 percent
So, since the refractive index of a clear solid is going to be much more similar to that of marmoleum than a gas like air, then much less light gets reflected at the nail_polish/marmoleum interface. Most of the reflected light comes from the air/nail_polish interface, which is smooth like the surrounding marmoleum.
Since you only see that scratch because it's white, it will only be about 1/10th as visible if you cover it with a clear solid (like clear nail polish or whatever).
Bud Cline's response (suggesting to "wax" the floor) would have worked, but you don't need to wax the whole Marmoleum floor, you just need to "wax" that scratch.
Ideally, it would be best to paint over that scratch with something which had the same refractive index as the Marmoleum (to effectively make the scratch disappear completely, but I don't know what the refractive index of Marmoleum is, let alone if there's a chemical that would dry to a solid of that same refractive index.
And, of course, it doesn't need to be nail polish. Anything that will dry to a clear solid would work, like an acrylic floor polish or sealer, a clear water based wood varnish like Minwax's "Polycrylic" or Flecto's "Diamond" water based varnish. An oil based polyurethane would probably work too, but it would add a yellowish appearance to the scratch cuz it'll dry slightly yellow in colour.
You can also just paint over that scratch with water to get a ballpark idea of what will happen with clear nail polish. The refractive index of water is only about 1.33, whereas that of a clear solid would be higher, but it will give you an albeit pessimistic idea of how much of an improvement to expect.