To scrape or rub off your feet would mean that the action was so vigorous that you didn't have any feet when you were done.
"... don't forget to scrape your shoes off...." or "...don't forget to scrape the dirt off your shoes..." would sound better to me. If the person is barefooted, I suppose you could say, "...don't to wipe your feet off on this mop (or that carpet)..." I would make sure to break up the phrasal verb to make it sound more like an idiom than a literal direction.
Is it common where you are to have mops for scraping the dirt off your feet? Something like this?