A system and method for flexible multiple protocols are presented. A device's logical layer may be dynamically configured on a per interface basis to communicate with external devices in a coherent or a non-coherent mode. In coherent mode, commands such as coherency protocol, system commands, and snoop response pass from the device's internal system bus to an external device, thereby creating a logical extension of the devices internal system bus. In non-coherent mode, the input-output bus unit receives commands from the internal system bus and generates non-coherent input-output commands, which are eventually received by an external device.