A method, system, and computer program product for two-sided, dynamic cache injection control are provided. An I/O adapter generates an I/O transaction in response to receiving a request for the transaction. The transaction includes an ID field and a requested address. The adapter looks up the address in a cache translation table stored thereon, which includes mappings between addresses and corresponding address space identifiers (ASIDs). The adapter enters an ASID in the ID field when the requested address is present in the cache translation table. IDs corresponding to device identifiers, address ranges and pattern strings may also be entered. The adapter sends the transaction to one of an I/O hub and system chipset, which in turn, looks up the ASID in a table stored thereon and injects the requested address and corresponding data in a processor complex when the ASID is present in the table, indicating that the address space corresponding to the ASID is actively running on a processor in the complex. The ASIDs are dynamically determined and set in the adapter during execution of an application in the processor complex.