Cache Coherency in Computer Architecture is defined as the uniformity of the shared resources data that ends up with stored in different local cache.

Now. let's understand it with an example.
We all use social medias or different type of application in our smart phones on a regular basis. When we open any application in smart phones, the data is collected in the memory of our smart phones. Now the question arises, which memory ? So the simple answer is data is stored in two different memories - the first one is Main Memory and the second one is Cache Memory. The main memory obviously we all know, And the cache memory is the memory which is temporary memory and some relevant data related to application stored in it. That's what the cache memory is and this concept is called as Cache Coherence.