Memory device and refresh information coherence method thereof

A memory device includes a memory with a plurality of memory blocks and a first storage circuit to store a first data table and a first refresh value, and a memory controller with a second storage circuit to store a second data table and a second refresh value. When the memory controller meets a refresh request, the memory controller reads the second refresh value and compares the corresponding access address to the corresponding bit in the second data table to determine whether valid data are stored in a specific memory block of the memory. The memory controller sends a valid-data refresh command to the memory when valid data are stored in the specific memory block, but sends an invalid-data refresh command to the memory when invalid data are stored in the specific memory block.