Jacques said "consistency", not "coherency"… those are different things. Yes, most processors provide a coherent cache – individual writes are guaranteed to be

Jacques said "consistency", not "coherency"… those are different things. Yes, most processors provide a coherent cache – individual writes are guaranteed to be eventually seen by all cores. However, most modern processors do not provide a consistent cache (for performance's sake): the order that unrelated writes become visible is not guaranteed. Memory fences (which are not flushes or invalidates; neither implies the other!) instruct the CPU to provide such ordering.