memory hierarchy as well. This policy ensures that the data is stored safely as it is written throughout the hierarchy.

However, in the case of the write back policy, the changed cache block will be updated in the lower-level hierarchy only when the cache block is evicted. A "dirty bit" is attached to each cache block and set whenever the cache block is modified. During eviction, blocks with a set dirty bit will be written to the lower-level hierarchy. Under this policy, there is a risk for data-loss