What was found
DURING CRUISE FLIGHT VTK AND MAP FLAGS APPEARED ON LEFT NAV DISPLAY. BOTH CDU'S WENT TO MENU SCREENS. FIRST OFFICER'S NAV DISPLAY INDICATED A DRIFT .7-.8 NM RIGHT OF CRUISE. FAILURE WENT AWAY AND BOTH NAV DISPLAYS RETURNED TO NORMAL. GROUNDED - YES. FMCS BITE SHOWED PROGRAM FAULT LOGGED FOR LAST LEG. ACCOMPLISHED RESET AND TEST PER B737-800 FIM 34-61 TASK 807 AND FMCS OPERATIONAL TEST PER B737-800 AMM 34-61-0-710-801- ALL TESTS PASS.