I had a block corruption of my primary database, though we had a standby build we wanted to recover the Primary instead of failover to the Standby.
This recovery is possible when you have say a full backup made of the database till 9th May and all archivelogs from 9th May till 12th MAY are present.
Put the database in mount mode and restore it till the time before the corruption happened.
run {
set until time to_date('12-May-2012 00:00:00', 'DD-MON-YYYY HH24:MI:SS');
restore database;
recover database;
}