No consume-available filter is scratch-proof. I do not know of any special application filter that is scratch-proof either, but you might find those fitted into housings made of tempered glass for diving, industrial or aeronautical applications.
Most of the time, what gets damaged on consumer-application filters is the coatings.
If got budget, I would get a Rodenstock filter. Costs about twice as much as a B+W MRC, but worth it if you want one of the best filters. Rodenstock is a company with a far longer history of manufacturing top-of-the-line optics than Schneider.
I like the range of Nikon multi-coated filters, after that, any of the high-end filters like Hoya HD, Pro-1 digital, SHMC, B+W. Some folks in the US like Heliopan and Tiffen for high-end filters, but I've never tried them so I can't comment.
Note: IIRC, there have been some reports (here on CS) of Hoya HD's cracking or breaking. No dropping or fall, just crack from being screwed in or something like that.
I've had a B+W XS pro scratched as well..All these filters are marketed as scratch resistant to certain extent and not completely scratch proof! Personally I find little difference between Hoya HD and B+W XS Pro. On a rare occasion one of my Hoya HD produced a nasty flare but I couldn't reproduce it again..Just my 2 cents..