In the past, I used this technique from TAC to delete persistent devices:
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http://ciscoworks:1741/dbreader/dbreader.html
username: dba
db password= your password
db name=rme
DEV_FQN
DEV_RELOAD
DEV_RLD_HIST
get db tables (DEV_FQN, DEV_RELOAD and DEV_RLD_HIST)
here's the procedure
1. Login to dbreader
2. check DEV_FQN and take note on the Device_Id column
3. List the Device_ID you want to delete
4. Go back to AdHoc Retrieval Page by using the back button of your browser
5. Input the credentials plus the execute sql staement
delete from DEV_FQN where Device_Id = x
where x is the Device_Id of the device you want to delete.
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YMMV.