I would first give it a good cleaning. Perhaps a bit (but not much) more agressive than what bdial says. Lens coatings are very durable, and I have seen lenses that looked pretty bad be fine with a good cleaning.
I looked at a 20mm Nikon lens at a camera show, and thought the coating was damaged. The booth owner wet his thumb and scrubbed the lens to show me it was just dirt. Bought the lens, gave it another good cleaning and there is no visible scratches or 'cleaning marks'. Just shows one shouldn't give up to easily.