A method, system, and computer program product for data transfer to memory over an input/output (I/O) interconnect are provided. The method includes reading a mailbox stored on an I/O adapter in response to a request to initiate an I/O transaction. The mailbox stores a directive that defines a condition under which cache injection for data values in the I/O transaction will not be performed. The method also includes embedding a hint into the I/O transaction when the directive in the mailbox matches data received in the request, and executing the I/O transaction. The execution of the I/O transaction causes a system chipset or I/O hub for a processor receiving the I/O transaction, to directly store the data values from the I/O transaction into system memory and to suppress the cache injection of the data values into a cache memory upon presence of the hint in a header of the I/O transaction.