As can be seen in the figure , if the top client has a copy of a memory block from a previous read and the bottom client changes that memory block , the top client could be left with an invalid cache of memory , without knowing . Referring to the `` Multiple Caches of Shared Resource '' figure , if the top client has a copy of a memory block from a previous read and the bottom client changes that memory block , the top client could be left with an invalid cache of memory without any notification of the change .