1. A method of data processing in a data processing system including a processor core, a system memory coupled to the processor core, an input/output adapter (IOA), and an input/output (I/O) host bridge, the method comprising: the I/O host bridge receiving I/O messages from the processor core in a register; the I/O host bridge receiving I/O messages from the IOA in a buffer; and the I/O host bridge forming a stream of I/O messages from those received in the register and the buffer; and the I/O host bridge servicing I/O messages from the stream.