Drop the database and the backups using RMAN client

1.startup the database in mount exclusive mode

export ORACLE_SID=CVRMAN
 sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Tue May 13 08:53:17 2014

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup exclusive mount;
ORACLE instance started.

Total System Global Area  730714112 bytes
Fixed Size                  2256832 bytes
Variable Size             452984896 bytes
Database Buffers          272629760 bytes
Redo Buffers                2842624 bytes
Database mounted.
SQL>exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, Automatic Storage Management, OLAP, Data Mining
and Real Application Testing options

2.Enable restricted session

[oracle@mfa-solcomp-poc05 ~]$ rman target "/"

Recovery Manager: Release 11.2.0.4.0 - Production on Tue May 13 08:57:31 2014

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.

connected to target database: CVRMAN (DBID=657566608, not open)

RMAN> sql "alter system enable restricted session";

using target database control file instead of recovery catalog
sql statement: alter system enable restricted session

3.Drop the database including backups

RMAN> drop database including backups;

database name is "CVRMAN" and DBID is 657566608

Do you really want to drop all backups and the database (enter YES or NO)?YES