public static void emergencyClose() {
    ConnectionTable ct = lastInstance.get();
    if (ct == null) {
      return;
    }
    lastInstance.set(null);
  }
Clears lastInstance. Does not yet close underlying sockets, but probably not strictly
necessary.

@see SystemFailure#emergencyClose()
geode-core/src/main/java/org/apache/geode/internal/tcp/ConnectionTable.java