to analice and get access remote out of my domain

to analice and get access remote out of my domain

How I can analice and get access remote of all machine that not belong to my domain?
for example in my organization there are visitors of other companies and their domains are differents to mi company domain. I don't have the active directory of those companies, by network the scan it works, but I can not get Access remote the message error is: ERROR:No response received from workstation. Probably the workstation might be switched off or does not exist.
What I need to configure. because I do averything on the help of Service Desk
thanks

                New to ADSelfService Plus?