I presume you have a server that has the TAPEUTIL utility (NTUTIL on NT).
If so, there is a capability to "erase" the tape using the same
functionality as the mainframe dataset erase (DSE) otherwise know as Erase
on Scratch with RACF.  This can also be issued in a batch mode.  The Magstar
Installation and User's Guide has the information on how to use the utility.

Hope this helps.