JBoss.orgCommunity Documentation
It's JBossCache class registered as eXo container component in configuration.xml file.
  <component>
     <key>org.jboss.cache.transaction.TransactionManagerLookup</key>
     <type>org.jboss.cache.transaction.JBossStandaloneJTAManagerLookup</type>
  </component>JBossStandaloneJTAManagerLookup used in standalone environment. Bur for Application Server environment use GenericTransactionManagerLookup.