A read allocation indicator (e.g. read allocation signal 30) is provided to storage circuitry (e.g. cache 22) to selectively determine whether read allocation will be performed for the read access. Read allocation may include modification of the information content of the cache (22) and/or modification of the read replacement algorithm state implemented by the read allocation circuitry (70) in cache (22). For certain types of debug operations, it may be very useful to provide a read allocation indicator that ensures that no unwanted modification are made to the storage circuitry during a read access. Yet other types of debug operations may want the storage circuitry to be modified in the standard manner when a read access occurs.