code: private void removeAllBroadcasts(Set<String> sessionIds) {
  
          if (sessionIds == null) {
              for (CmsSessionInfo info : OpenCms.getSessionManager().getSessionInfos()) {
                  OpenCms.getSessionManager().getBroadcastQueue(info.getSessionId().getStringValue()).clear();
              }
              return;
          }
          for (String sessionId : sessionIds) {
              OpenCms.getSessionManager().getBroadcastQueue(sessionId).clear();
          }
      }
docs: Removes all pending broadcasts
  
  @param sessionIds to remove broadcast for (or null for all sessions)