Apache Solr Multi-core Setup on Tomcat

Setting up one Solr server with two or more Drupal sites takes some additional configuration. If this is not done, all of the data for each site goes into the same index and when searching on one site, results are returned from both sites. If that's not the desired result (faceting won't currently work correctly), then it is necessary to set up a separate Solr core for each site. Each core is a totally independent search index.