AutoCAD .NET :: Identify Presence Of Block In Particular Layout

I have to insert a block in a paerspace layout if it is not already present in that layout. I tried the following function to identify the presence of the block.

But it returns true even if the block is not present in the particular layout but is present in another layout.

private bool checkBlockPresence()
{
try
{
Autodesk.AutoCAD.EditorInput.Editor ed = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.Editor;
[code]........

Also I am using the following function to make the particular layout active before calling the above function.

public void SwitchTo(string Layout)
{
Autodesk.AutoCAD.ApplicationServices.Document acDoc = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;
Autodesk.AutoCAD.DatabaseServices.Database acCurDb = acDoc.Database;
using (Autodesk.AutoCAD.ApplicationServices.DocumentLock doclock = acDoc.LockDocument())
[code].......           

So my code is similar to

SwithTo("A3")
if(checkBlockPresence() == false)  // this always returns true.
{
---------
}