As each processor module receives the broadcast data, it updates the contents of the affected cache block if this block is present in its cache.

Write through with invalidation of copies :

When a processor writes a new value into its cache, this value is written into the memory module, and all copies in the other caches are invalidated. Again broadcasting can be used to send the invalidation requests through the system.

Write back protocol:

In the write-back protocol, multiple copies of a cache block may exist if different processors have loaded (read) the block into their caches.

If some processor wants to change this block, it must first become an exclusive owner of this block.

When the ownership is granted to this processor by the memory module that is the home location of the block. all other copies, including the one in the memory module, are invalidated.

Now the owner of the block may change the contents of the memory.