There are several servers we do not want to scan but need to keep on the asset list

There are several servers we do not want to scan but need to keep on the asset list

But, 
Workstation(s)/Server(s) failed during last scan.
list is keep comes back whenever I scan the servers. 
Those specific servers are just for record purpose and outside of the domain. (also blocked by firewall due to the company policy)

How can I keep those servers / workstations away from Failed scan list? 

Thank you in advance. 

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