After running into an issue with the mdl_question_state table in 1.9.3 (yeah I know... we are upgrading this Fall), I found the only safe way to purge all 10gigs of data in it is to do course resets. Unfortunately, we never had a policy in place to consistantly reset courses after each semester
I am sort of surprised that there isn't already a mass course-reset option available. I think it would be beneficial to all parties; administrators wouldn't have to worry about enforcing a course reset policy for each single person and users (instructors) wouldn't have to worry about remembering to reset their courses.
I've created a ticket in the tracker for this new feature that has other details in it, but I figured I'd also advertise and open discussion for it here.
My university is currently getting the go-ahead to allocate some resources towards building a tool for doing this but it will be somewhat crude, won't have a UI, and will only be designed to work with 1.9. The next step might be to make it more user friendly.
By the way, I found this bit of code that supposedly does what I'm looking for. I'm in the process of modifying it to pick out courses by itself (instead of manually inputting them). http://stackoverflow.com/questions/1061563/how-do-i-delete-course-enrolments-in-moodle-in-bulk