Recargar opciones de listbox

[KarielYagami]

Hola buen dia

Tengo 3 list box uno llamado region, otro pais y otro lugar, el de region, muestra los continentes del mundo, el segundo los paises dependiendo del continente y lugares dependiendo del pais, el problema que tengo es que cuando eligo otra opcion y quiero volver a filtrar aparecen lugares que ya habia borrado, pero vuelvo a elegir continente o pais y de nuevo el pais elegido primeramente, y ya no aparecen, osea que hago un refresh manual

Quiero preguntar si es posible que este refresh se haga de manerea automatica

Código:

capturefor (javascript)
	<script type="text/javascript">/*<![CDATA[*/
		$(document).ready(function() {
			$('select#dashboard_Location_Region_Id').change(function() {
					var selector = 'select#SubRegion_Id';
					var url = siteURL + '/system/location/GetSubRegionByRegion.ashx';
					var url_params = { id: $(this).val() };
 
					GetJSONSelectOptions(url, url_params, selector, 'Id', 'Name');
					CleanSelectOptions('select#SubRegion_Id');			
					
										
					GetCountriesByRegion($(this).val());
				});						
				
			$('select#SubRegion_Id').change(function() {
					var selector = 'select#dashboard_Location_Country_Id';
					var url = siteURL + '/system/location/GetCountryBySubRegion.ashx';
					var url_params = { id: $(this).val(), region_id: $('select#dashboard_Location_Region_Id').val() };
 
					GetJSONSelectOptions(url, url_params, selector, 'Id', 'Name');				
					CleanSelectOptions('select#dashboard_Location_Country_Id');				
					
					$('select#entity_Location_Country_Id option:empty').remove();
					
				});	
				
			$('select#dashboard_Location_Country_Id').change(function() {
					var rel = $(this).attr('rel');
					var relSelector = HTMLRelSelector(rel);
					var selector = 'select#dashboard_Location_Site_Id' + relSelector;
					var url = siteURL + '/system/location/GetSitesByCountry.ashx';
					var url_params = { id: $('select#dashboard_Location_Country_Id' + relSelector).val() };

					GetJSONSelectOptions(url, url_params, selector, 'Id', 'Name');
					CleanSelectOptions('select#dashboard_Location_Site_Id');
					
					$('select#entity_Location_Site_Id option:empty').remove();
				});	
				
		});		
		
		
		function GetCountriesByRegion(region_id)
		{
			var selector = 'select#dashboard_Location_Country_Id';
			var url = siteURL + '/system/location/GetCountriesByRegion.ashx';
			var url_params = { id: region_id };
			
			GetJSONSelectOptions(url, url_params, selector, 'Id', 'Name');	
			CleanSelectOptions('select#dashboard_Location_Site_Id');
			$('select#entity_Location_Site_Id option:empty').remove();
			CleanSelectOptions('select#Region_Id');
			CleanSelectOptions('select#dashboard_Location_Country_Id');	
			CleanSelectOptions('select#dashboard_Location_Site_Id');	
			$('select#entity_Location_Site_Id option:empty').remove();			
		}
		
	
		
	/*]]>*/</script>
#end

#blockcomponent (Page with "pagetitle=Checklist by Location: Completeness Percentage $title")
	#mainbuttonsbar
        $ButtonHelper.ExportToExcel()
        $ButtonHelper.MailTo()
        $ButtonHelper.SaveReport()
    #end
    
    #filter
        #blockcomponent (Filter with "action=list" "method=get")
            #if (!$filterOwnLocationOnly)

les envio parte del codigo por si me pueden ayudar

gracias