Flex 4 ~ set s:Scroller to top

MXML
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<s:Scroller x="325" y="150" id="ContentScrollWrapper" width="640" height="440" horizontalScrollPolicy="off" >

<s:Group id="ContentWrapper" >
</s:Group>

</s:Scroller>

Action Script
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ContentScrollWrapper.viewport.verticalScrollPosition = 0;



reference
http://stackoverflow.com/questions/1346993/flex-4-sscroller-how-to-bring-contained-component-into-view