Is it possible to have different instance of Solr - one pointing to the staging website while other pointing to production website while the CMS sytem is common to both Solr instance. I am not checking about high availability or scaling or solr but want to have two separate solr instance so that staging envrironment can be completely separate from production CD environment in DMZ zone with no linking to internal environments like staging.
As far as I know one Sitecore CM instance can only index to one SOLR instance. If you want it to index to two different SOLR instances that you want to use, then you need to find a way to replicate between those two SOLR instance. You point your CM to SOLR instance A, then you replicate that to SOLR instance B.