It doesn't matter who the channel belongs to; just put the channel name in the target parameter, and the script should trigger there... eg:
Code:
on *:TEXT:*help*:#donotaskforhelp:{ }

will trigger when "help" is found in a msg sent to #donotaskforhelp

Code:
on @*:TEXT:*damn*:#donotsaydamn:{ ]

will trigger when "damn" is found in a msg set to #donotsaydamn and the client with the script is an op.

As long as the client with the script is joined to the channel in question, the script will trigger (or at least attempt to) when appropriate.

Just be careful, because some channels won't want you to use scripts in their channels.