Abstract: A memory management unit includes a translation buffer unit for storing memory management attribute entries that originate from a plurality of different memory management contexts. Context disambiguation circuitry responds to one or more characteristics of a received memory transaction to form a stream identifier and to determine which of the memory management context matches that memory transaction. In this way, memory management attribute entries stored within the translation lookaside buffer are formed under control of the appropriate matching context. When the translation buffer unit receives a further transaction, then a further stream identifier is formed therefrom and if this matches the stream identifier of stored memory management attribute entries then those memory management attribute entries may be used (if appropriate) for that further memory transaction.