Flush agent setup for multiple farm in single dispatcher

The Dispatcher Flush replication agent on the AEM publish instance must send invalidation requests to the correct Dispatcher farm. To target a farm, use the URI property of the Dispatcher Flush replication agent (on the Transport tab). Include the value of the /virtualhost property for the Dispatcher farm that is configured for invalidating the cache:

https://*webserver_name*:*port*/*virtual_host*/dispatcher/invalidate.cache

For example, to use the farm_flush farm of the previous example, the URI is 

https://localhost:80/invalidation_only/dispatcher/invalidate.cache 

For Dispatcher Flush agents, the URI property is used only if you use path-based virtualhost entries to differentiate between farms. You use this field to target the farm to invalidate. For example, farm #1 has a virtual host of 

www.mysite.com/path1/* and farm #2 has a virtual host of www.mysite.com/path2/* . You can use a URL of /path1/invalidate.cache to target the first farm and /path2/invalidate.cache to target the second farm.

More details at [1]

[1] https://docs.adobe.com/content/help/en/experience-manager-dispatcher/using/configuring/page-invalidate.html#invalidating-dispatcher-cache-from-the-authoring-environment

https://docs.adobe.com/content/help/en/experience-manager-dispatcher/using/configuring/dispatcher-domains.html#configuring-the-dispatcher-flush-replication-agent

For example, we have mysite1, mysite2 and mysite3 in single publish instance and each site has its own flush agent. How should we configure flush rule so that any page activation in mysite1 will only trigger mysite1 flush agent and not the other two ?