Delete the old ASM database file from its original location

$ ORACLE_SID=+ASM; export ORACLE_SID

$ sqlplus "/ as sysdba"

SQL> ALTER DISKGROUP TESTDB_DATA2 DROP FILE '+TESTDB_DATA2/testdb/datafile/app_data.256.598127837';


http://www.idevelopment.info/data/Oracle/DBA_tips/Automatic_Storage_Management/ASM_36.shtml