Scrolling problem with background using View/Scene

[nileshsince1980]

Hi,
I am using view/Scene architecture to show rectangels and lines with background picture.
I have drawn background in GraphicsScene::drawBackground(..) function.
To speed up rendering I have set cache background

view->setCacheMode(QGraphicsView::CacheBackground);

view->setCacheMode(QGraphicsView::CacheBackground);

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But using this when I zoom and then scroll the content there is artifacts comes. After scrolling scene doesnt refresh property.Background image doesnt refresh.

I have tried using

GraphicsView::scrollContentsBy(int dx, int dy)
{
   scene()->invalidate(sceneRect(), QGraphicsScene::BackgroundLayer);
   QGraphicsView::scrollContentsBy(dx, dy);
}

GraphicsView::scrollContentsBy(int dx, int dy)
{
   scene()->invalidate(sceneRect(), QGraphicsScene::BackgroundLayer);
   QGraphicsView::scrollContentsBy(dx, dy);
}

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But this also doesnt refersh the screen.
I want to refresh only portion which is visible because of scrolling.
Can anybody have solution for this.