ECMAScript object model can only be used in SharePoint sites. So you can’t use this object model in an asp.net site to access SharePoint resources deployed in another url as this is cross-site scripting and not allowed.
But on a master page of the root site, can we access the lists present on the other sites in site collection and the lists present on sites in another site collection?
You cannot make cross-sitecollection calls from javascript client object model in SharePoint 2010.
But you can make such calls in SharePoint 2013:
var crossSiteContext = new SP.ClientContext("http://url-of-another-siteCollection/");
var crossSiteWeb = crossSiteContext.get_web();
crossSiteContext.load(crossSiteWeb);
crossSiteContext.executeQueryAsync(function(){
alert(crossSiteWeb.get_title());
},function(sender,args){ alert(args.get_message()); });
