DATA TRANSFER UNIT WITH SUPPORT FOR MULTIPLE COHERENCY GRANULES

A data transfer unit is able to read data from a source at the source coherency granule size and write data at the destination coherency granule size even though the two granule sizes may be different. A data transfer unit has registers for storing the granule size information in preparation of performing a transfer of a data block between a source and a destination. The data block is transferred in sub-blocks. Except for the first and last sub-blocks, the sub-blocks, for a read, are sized to the source coherency granule size, which is the transfer size that has been optimized for the source. For the write, the sub-blocks are sized to the destination coherency granule size, which is the transfer size that has been optimized for the destination. Thus, both the read and the write are optimized even though the transfers themselves are among devices with different coherency granules.