Hello Charles Garber,
Thank you for posting in Q&A forum.
As I understand, the server you mentioned is in one workgroup instead of one domain, am I right?
What do you mean "keep the log credentials"? I understand if one user signed in the machine in the past, and you do not delete this account and its user profile in the machine, then the account and the same profile will be kept in this machine.
You can delete only all the data about your business on this server.
If your business data is not stored in C disk, you can format all other disks (like D, E, F) except C.
I hope the information above is helpful.
If you have any questions or concerns, please feel free to let us know.
Best Regards,
Daisy Zhou
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