A processor prevents writeback race condition errors by maintaining responsibility for data until the writeback request is confirmed by an intervention message from a cache coherency manager. If a request for the same data arrives before the intervention message, the processor core unit provides the requested data and cancels the pending writeback request. The cache coherency data associated with cache lines indicates whether a request for data has been received prior to the intervention message associated with the writeback request. The cache coherency data of a cache line has a value of “modified” when the writeback request is initiated. When the intervention message associated with the writeback request is received, the cache lines's cache coherency data is examined. A change in the cache coherency data from the value of “modified” indicates that the request for data has been received prior to the intervention and the writeback request should be cancelled.