1. A memory system, comprising: a resistive nonvolatile memory array; a memory array; and a memory controller configured to: read data stored in the resistive nonvolatile memory array; write the data read from the resistive nonvolatile memory array, and an indicator bit to the memory array, the indicator bit indicating whether data stored in the memory array are valid; determine whether the indicator bit is valid; and write the data stored in the memory array to the resistive nonvolatile memory array when the indicator bit is valid.