So what if you want to use a username and password that is not understood by your local system. I came across that issue today and the solution is quite simple ... but you have to know it can be done.
first establish a IPC connection to the target system
NET USE \\<TargetSystemIP/Name>\IPC$ <UserPassword> /USER:<Domain>\<UserName>
then issue the reboot command via that
shutdown /r /t 3 /c " <comment for reboot> " /m \\<TargetSystemIP/Name>
wait a moment and the target system will reboot