I recently made a couple of bootable usb drives on my MacBook Pro. These drives are now long ago ejected and does not show anywhere in my operating system. BUT in Media Browser they still show up as if they were mounted disks.
It is only in Premiere Pro i see them so i guess i want to erase settings somewhere to get rid of them.
I have reinstalled Premiere Pro but they still show up after that.
Not sure about Media Browser, but Bridge uses Cache files for keeping track of HDD's, both external and internal. I suspect that something similar is being done by MB, but will wait for a clarification from an Adobe Staff member, or user with more direct knowledge, than I have.
In Bridge, on has the option to locate the Cache files, where they want them, and then to also clean those files.
The Cache cleaning/deleting in PrPro is pretty specific to Project, as far as I know, but you might was to look on your system for MB Cache files too.
Similar can happen with other file cataloging software. I found that ThumbsPlus still had info on several DVD-Media discs, that had been scanned long ago, though none had been back in the multi-drive for many months. I cleaned its Cache files, and those references disappeared.