The cache is 100% Apple/iOS code that should free up if you're running low on device space.
I researched a bit ago and it is possible to force clear, I think, but its a low priority because it's not a bug, it's iOS using unused device space for caching.
Really the bug is that cache is exposed as 'used space' in the interface anyways. iOS should show cache as free space (because it just gets cleared when you need the space anyways).