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

SQL> exit

rman target /

RMAN> drop database including backups;