onsider a system that has multiple processors in which each processor has its own cache, but main memory is shared among all processors.

Which cache write policy would you use?

With regard to this system, what problems are caused if a processor has a copy of memory block A in its cache and a second processor, also having a copy of A in its cache, then updates main memory block A$?$ Can you think of a way $($perhaps more than one$)$ of preventing this situation, or at least of lessening its effects?