The answer is we need cache coherence. Cache coherence is defined as the uniformity of shared resource data that ends up stored in multiple local caches. In other words, we must keep all the local caches synchronized. The challenge of doing so is known as the Cache Coherence Problemcache coherence problem. To solve this problem, multi-processor systems rely on cache coherence protocols to manage and maintain the cache. While the details of these protocols are beyond this assignment scope, more information on cache coherence protocols can be found here: https://en.wikipedia.org/wiki/Cache_coherency_protocols_(examples).