how know that scroll is in the end of the list

I have listbox with item and scrollviewer for the list.
The scroll appears only whan the user scrolls with his finger.
I want to display an indication with an icon that he can scroll and hide the icon when he reaches the last item.

me code In short:

<ScrollBar x:name="PART_VerticalScrollContentPresenter" 
value="{Binding VerticalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}"
Maximum="{templateBinding ScrollableHeight}"/>

<ControlTemplate.Triggers>
<dataTrigger Binding="{Binding Value, ElementName=PART_VerticalScrollBar}" Value="Maximum">
<DataTrigger.EnterActions>
<BeginStoryboard x:name="StoryBordScrollDown" Storyboard="{StaticResource StoryBordScrollDown}"/>
</DataTrigger.EnterActions>
</DataTrigger>

<Trigger Property="Value" Value="0" SourceName="PART_VerticalScrollBar">
<DataTrigger.EnterActions>
<BeginStoryboard x:name="StoryBordScrollUp" Storyboard="{StaticResource StoryBordScrollUp}"/>
</DataTrigger.EnterActions>

the second Trigger work fine the first Trigger Not working