Cache logic associated with a respective one of multiple processing threads executing in parallel updates corresponding data fields of a cache to uniquely mark its contents. The marked contents represent a respective read set for a transaction. For example, at an outset of executing a transaction, a respective processing thread chooses a data value to mark contents of the cache used for producing a transaction outcome for the processing thread. Upon each read of shared data from main memory, the cache stores a copy of the data and marks it as being used during execution of the processing thread. If uniquely marked contents of a respective cache line happen to be displaced (e.g., overwritten) during execution of a processing thread, then the transaction is aborted (rather than being committed to main memory) because there is a possibility that another transaction overwrote a shared data value used during the respective transaction.