Actually, foreign Central Banks don't even need to dump treasuries to require QE Infinity - they can just reduce or stop absorbing the continual outflow of debt emitted by the USG.
The USG has a trillion dollar+ yearly budget deficit. If central banks don't absorb that outflow of debt then either the USG reduces its spend (as if, those NSA datacentres aren't cheap), interest rates go up (USG will need will need even more debt to pay its debt) or the fed continues to buy it all up.