AT LOCAL
The AT LOCAL expression converts the source data into the local time equivalent:
SQL> SELECT FROM_TZ(
2 CAST(TO_DATE('2012-12-01 11:00:00','RRRR-MM-DD HH:MI:SS') AS TIMESTAMP), 'America/Los_Angeles'
3 ) AT LOCAL "East Coast Time"
4 FROM DUAL;
East Coast Time
---------------------------------------------------------------------------
01-DEC-12 11.00.00.000000 AM PST
SQL>