If CL>TL, then the activity level CL is compared to the level of activity on the system bus (CS) and, if CL>CS, the system bus is selected; otherwise, the local bus is selected. (As in other embodiments, the case where CL=TL can be treated as CL>TL or CL<TL, as desired.)In other embodiments, steering control circuit 314 may also select among mirror locations based on factors other than the measure