Replicating reduces contention among processors for shared data values.
As each processor view the memory through its cache, system must find a way to ensure that different processors do not have different values for the same memory location.
Cache coherence problem: CPU has an obsolete image of an address location stored in its cache.
Snooping Protocol is often used to maintain cache coherence: Each CPU cache’s controller will monitor (snoop) the bus to see which cache blocks are being requested by other CPU.