A cache in a data processing apparatus has a status field associated with each entry in the cache to store a security value indicative of whether the data stored in that entry are secure data, non-secure data or aliased data. Secure data are only accessible in response to a secure data access request, non-secure data are only accessible in response to a non-secure data access request and aliased data are accessible in response to either a secure or a non-secure data access request. The data processing apparatus also has bus fabric which provides security data in response to a bus access request, the security data being indicative of whether the bus access request is to a storage location designated as secure, non-secure or aliased.