= undefined) {
      // Clean up Bokeh references
      var cmd = "from bokeh.io.state import curstate; print(curstate().uuid_to_server['" + server_id + "'].get_sessions()[0].document.roots[0]._id)";
      cell.notebook.kernel.execute(cmd, {
        iopub: {
          output: function(msg) {
            var id = msg.content.text.trim();
            if (id in Bokeh.index) {
              Bokeh.index[id].model.document.clear();
              delete Bokeh.index[id];
            }
          }
        }
      })