The answer to this question is getting something else stuck in it. or stare at a grass blade for hours and think of nothing else. It's never worked for me, but who knows, might work for you.
I always have some kind of music piece stuck in my head. whether it's classical, soundtrack, one of my favorite songs at the moment or some annoying little ditty from my childhood. there is ALAWAYS something stuck in my head. I wish sometimes i could figure out how to turn off that mental CD player stuck on repeat. Bother.