How to un-register database from RMAN repository

oracle@myunxsrv:/oracle>sqlplus rmanadmin/rmanadmin@rmandb

SQL> select * from rc_database;

   DB_KEY  DBINC_KEY       DBID NAME     RESETLOGS_CHANGE# RESETLOGS
   ———————————————————————————-
     82740      82741 4068072203 DB1            1833108725 15-NOV-05

    109899     109900 3178819647 MYDB           1839426791 23-NOV-05

    506581     506582 3053438738 ORAGRID            157703 01-MAY-07

         1          2 1637292221 EMULE                   1 10-JAN-05

12 rows selected.

SQL> exec dbms_rcvcat.unregisterdatabase( 1, 1637292221 );

PL/SQL procedure successfully completed.