How do you correct a corrupted index in Oracle?
There is a command line utility dbv which can scan a datafile a will report and mark corrupted blocks. If you want for "fix" it you can either use RMAN block recover option - if you run Ent. Edition and if you have RMAN backup.

Otherwise search for document named "How to format corrupted block" on Metalink. This describes a situation when a table block is corrupted but it is applicable for indexes too.
First of all you mast mark the block as corrupted.

PS: the is also an SQL comment "ALTER TABLE  VALIDATE STRUCTURE CASCADE", this will also generate a report, but will not fix anything.