Flushing cache lines doesn't work, at least not straightforwardly. The attacker can arrange things so that the cache line is pre-populated with something else t

Flushing cache lines doesn't work, at least not straightforwardly. The attacker can arrange things so that the cache line is pre-populated with something else that it has access to, with a colliding address that will be evicted by the speculative load. Flushing undoes the load, but can't easily undo the eviction.