Check point inside polygon (city boundary)

Currently, I am using World Geocoding Service(http://geocode.arcgis.com/arcgis/res.../GeocodeServer) and create a map extent to verify the address point whether inside the city boundary or not then show a pop up message. Map extent works great for xy boundary but point still show if the boundary is in irregular shape.
So how do you check if a point is inside a city boundary and using contains() from API reference?
if( polygon.contains( MapPoint(graphic.geometry) ) )

I modify showSearchResultOnMap function on GeocoderComponent.mxml.
Thank you.