There is provided an apparatus for receiving a request from a master to access an input address. Coarse grain access circuitry stores and provides a reference to an area of an output address space in dependence on the input address. One or more fine grain access circuits, each store and provide a reference to a sub-area in the area of the output address space in dependence on the input address. The apparatus forwards the request from the coarse grain access circuitry to one of the one fine grain access circuits in dependence on the input address.