What kind of wall and what type of finish is on the wall? For example, a smooth dry wall painted with a glossy "washable" paint might be what you need to start with. But if the wall is has a rough finish, like brick or concrete block, it may be impossible to clean, even if finished. There are some interior paints that are marketed as washable, like for children's rooms. I've heard of "graffiti-resistant" paints (or coatings) that resist the adherence of paint as long as one starts washing them quickly.
Is repainting the surface an option?
Joe