Exposing an interface between windows in Titanium

gistfile1.js

//error when the a table row is clicked in nearme_window.js
[WARN] Exception in event callback. {
    line = 59;
    message = "'undefined' is not a function (evaluating 'pub_win.update_pub_details('blah')')";
    name = TypeError;
    sourceId = 233027648;
}

//nearme_window.js
module.exports = (function() {
  var self    = this,
      pub_win = require('fb/ui/pub_window'),
      win     = gui.createWindow({ 
      	title: L('title_nearme')
      }),
      nav = Titanium.UI.iPhone.createNavigationGroup({ window: win });
      
  var refresh = function() {
    api.getNearbyPubs(function(response_json) {
		var table = Ti.UI.createTableView();
		createTableData(response_json, table);
		table.addEventListener('click', function(e){
			pub_win.update_pub_details(e.rowData);
			nav.open(pub_win, {animated:true});
		});			
		win.add(table);
    });
  }

//pub_window.js
var lbl_pub_name = null;

exports.update_pub_details = function(pub_list_row) {
	lbl_pub_name.text = pub_list_row.pub_name;
}

module.exports = function() {
  lbl_pub_name = Ti.UI.createLabel({
  ...
  return win;
}();