I share 6 drives with up to 6 PC's. If you do not select a drive to share, then it is not shared across your network.
However, users on the same PC, they will have access unless you change ownership and/or permissions for users in the security settings.
My advice is to take ownership of the drives, remove all users in the list, and then add only yourself with full permissions.
How to share:
How to take ownership of any item and set users or permissions per item.
How to take ownership of any item:
Right Click on any Item>>Properties>>Security Tab>>Advanced
You can see here that TRUSTED INSTALLER is the Owner and all the user names listed below that can run Disk Cleanup.
Now you take Ownership of the Item:
Now you select CHANGE next to OWNER.
Advanced>>Find Now>>Select your user account name in the list>>OK
Apply>>Verify OK. Now you are the Owner of that file cleanmgr.exe.
Now select Disable Inheritance.
(This removes all the users in the list. Enabling it again will replace them back into the list)
If it does not remove them, then manually remove each of them.
Now you MUST ADD Your Name to the User List:
Now select ADD>>Select a Principle>>Advanced>>Find Now>>Select your user account name in the list>>OK>>OK
Now select full control permissions box>>OK
Now you are the owner and the only user on the list with full permissions for Disk Cleanup..
RESTART PC