Hi,
Instead of blocking the sidebar from seeing all servers (which would block Mac ones in addition to blocking the PCs), I think I've found a solution that works.
I used to have the same problem at my house (random PC servers showing up when there are no PCs in the house) and I thought someone was hacking onto my network.
To solve the issue:
1. Go to System Preferences
2. Click on the Sharing icon under Internet & Wireless
3. Decheck Printer Sharing
I've found that by dechecking Printer Sharing, the strange PC server never shows up.
Hope this helps!