There is none. Titan fully resists all interrupts, but the stomps stop anyway. With 3 DRGs in a group, my WAR still interrupts just fine.
If you time it properly, the 4th won't go off either. Just doesn't seem that you can go any fewer than 3 stomps. Any time after that, you can clear it with a stun or silence.
They go up to like 12 if you don't use anything and wait long enough. I've died from stomps from 10k HP when the healers went down. Stomps kept coming and coming until even I was dead.