1. A method of mapping transactions from device-specific input/output (I/O) domains to a host domain, the method comprising: instantiating in storage accessible to an I/O memory management unit (IOMMU) a mapping data structure that separately codes for each of the device-specific I/O domains, mapping information including operation translations to be applied to transactions associated with an address translation window for a respective one of the device-specific I/O domains; specifying for at least a portion of an address translation window for a first one of the device-specific I/O domains, a first operation translation; and specifying for at least a portion of an address translation window for a second one of the device-specific I/O domains, a second operation translation, the second operation translation differing from the first.