What configuration needs to be in place in order for internal events from one splunk instance to be in the _internal index of another splunk instance?
I am approaching this as something that has surprised me, as it seems to be only a handful of events, and they are of all the normal groups.
You likely have a forwarder pushing its internal logs over to your indexer. Check the originating host's inputs.conf and outputs.conf files, and disable any entries you do not wish to keep.
Here is some more info about forwarders: http://www.splunk.com/base/Documentation/latest/Admin/Moreaboutforwarders