1. A logically partitioned computer system comprising: a plurality of processors; a memory coupled to the plurality of processors having a plurality of logical partitions designated by a partition manager; a memory block with a mirrored memory partner block having the same data in a first logical partition where the memory block and the mirrored memory partner block are allocated on physical memory chips; a memory error detection mechanism that monitors the occurrence of correctable and uncorrectable memory errors in the physical memory chips; when the memory error detection mechanism determines a number of correctable memory errors above a predetermined threshold occur when accessing one of the physical memory chips that contains a memory block, a memory relocation mechanism transparently relocates data from the memory block to a first newly allocated memory block; and when the memory error detection mechanism determines an uncorrectable error occurs in the memory block and when there is a mirrored memory partner block with no uncorrectable errors, the memory relocation mechanism uses the mirrored memory partner block as a data source for data for the memory block with the uncorrectable error and then relocates the data to a second newly allocated memory block to replace the memory block with the uncorrectable error.