In Compute Resources with a valid, working libvirtd resource; if the libvirtd daemon on the remote host is restarted, all foreman operations with the resource fail:

There was an error listing VMs: Call to virConnectNumOfDefinedDomains failed: internal error client socket is closed

This remains until the foreman rails app is restarted.

Here is an equivalent bug in the OpenStack Compute (Nova) project for reference purposes:
https://bugs.launchpad.net/nova/+bug/1154473