I have a DataGrid, populated with objects in an ArrayCollection. After updating one of the objects\' fields, I want the screen to update. The data source is not bindable,
invalidateList tells the component that the data has changed, and it needs to reload it and re-render it.
invalidateDisplayList tells the component that it needs to redraw itself (but not necessarily reload its data).
invalidateDisplayList() merely sets a flag so that updateDisplayList() can be called later during a screen update. invalidateList() is what you want.
http://livedocs.adobe.com/flex/2/langref/mx/core/UIComponent.html#invalidateDisplayList()