Effacement is what happens when something is erased or blotted out. If you hit your head hard enough, it might cause the effacement of your memory.
You can use this noun for things that are physically erased, like the rain's effacement of the chalk portrait you drew on the sidewalk. It can also be used for figurative erasing, like the effacement of a dancer's dreams when he doesn't win a spot in the ballet corps. Effacement comes from the verb efface, "to erase or obliterate," from the Old French esfacier, literally "to remove the face."