What was found
WHILE AT CRUISE FLIGHT, CAPTS ND SHOWED A "VTK" WITH A FAILURE OF THE MAP. BOTH CDU'S HAD NO "FMC" DISPLAYED. QRH ACCOMPLISHED. BEFORE MOVING THE FMC SELECT SWITCH, THE CAPTS SIDE WAS RESTORED BUT THE F/O SIDE LOST THE MAP DISPLAY. BOTH CDUS DISPLAYED AN "FMC" OPTION. FMC SOURCE SELECT SWITCH MOVED TO "BOTH ON L" AND NORMAL OPERATION WAS RESTORED. ACFT GROUNDED. REF AMM 34-61-02, R & R LT FMC COMPUTER. SOFTWARE TRANSFER AND OPS NORMAL, IAW AMM 34-61-02 AND AMM 34-61-00.