DROP DATABASE THROUGH RMAN
In Oracle Database 10gR1 Oracle introduced the RMAN command DROP DATABSE. This one simple statement has the ability to completely remove a database including all RMAN backups with the optional INCLUDING BACKUPS clause.
sqlplus “/ as sysdba”
SQL> shutdown immediate;
SQL> startup mount exclusive
SQL> alter system enable restricted session
rman target /
RMAN> drop database including backups;