Zombie cookies
I've tried removing them with the following method:
zombie cookie removal
navigate to: ~/Users/YourAccountName/Library/Safari/Databases/_IndexedDB
where ~ is top level drive where the system is stored
The folders in the _IndexDB directory will include the cookie names (i.e....news.yahoo.com_0) you want to delete.
send the entire folder to the trash and empty it.
Mac mini