How to cleanup flashback area size?

One product database's flashback area size was reached the threshold,

the current flashback settings&status for this database are:

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

db_recovery_file_dest                string      /u01/oradata/flash_recovery_area

db_recovery_file_dest_size           big integer 600G

FILE_TYPE    PERCENT_SPACE_USED PERCENT_SPACE_RECLAIMABLE NUMBER_OF_FILES

------------ ------------------ ------------------------- ---------------

CONTROLFILE                   0                         0               0

ONLINELOG                     0                         0               0

ARCHIVELOG                    0                         0               0

BACKUPPIECE                   0                         0               0

IMAGECOPY                     0                         0               0

FLASHBACKLOG              84.77                     54.78            1168

but the strange thing is that there are two flashback path under the db_recovery_file_dest:

[oracle@prdlisdb570] /u01/oradata/flash_recovery_area 1053> ls -ltr

total 0

drwxr-x---    7 oracle   oinstall        256 Nov  4 2010  LISDB

drwxr-x---    3 oracle   oinstall        256 Jan 18 2011  P_LISDB