What was found
AFTER INITIAL LEVEL OFF FMC LIGHT CAME ON ALONG WITH VTK ON CAPTAIN'S NAV DISPLAY AND BOTH FMC'S WENT BLANK. INDICATIONS LASTED ABOUT 5 SEC. THEN EVERYTHING WENT BACK TO NORMAL. SAME SEQUENCE OF EVENTS HAPPENED ABOUT 2.5 HRS INTO FLIGHT. JUST PRIOR TO DESCENT LOST BOTH FMC'S FOR ABOUT 3 MINUTES. CAME BACK ON BOTH SIDES ON THEIR OWN BUT HAD TO MANUALLY RELOAD ALL WEIGHTS AND ROUTE DATA. ACFT GROUNDED. DISCREPANCY CLEARED AFTER REBOOTING BOTH LT & RT FMC'S REF FIM TASK 34-61, TASK 804. NO FAULTS NOTED. OPENED & CLOSED 2 C/B'S ON P-18-2, P6-1 2 C/B'S, LT & RT FMC BITE TESTS OK. AMM 34-61-00-810-801, NO CURRENT FAULTS NOTED. CLEARS MEL 34-36K.