What was found
LEFT FMC FAILED FOR ABOUT 30 SECONDS AFTER 2 HOURS OF CRUISE FLIGHT. LEFT FMC RETURNED TO NORMAL OPERATION WITH NO ACTION ON OUR PART. 30 MINUTES LATER, RIGHT FMC FAILED FOR 30 SECONDS THEN SELF-CORRECTED. 15 MINUTES LATER WE HAD DUAL FMC FAILURE FOR LESS THAN FIVE MINUTES ,THEN SELF-CORRECTED. GROUNDED - YES. PER CREW BOTH FMC'S RETURNED TO NORMAL. PER B737-900 AMM 34-63-00 THIS IS KNOWN AS A NUISANCE FAULT. ACCOMPLISHED FMC BITE CHK REF B737-900 FIM 34-61 TASK 801 OPS CHECK NORMAL.