AutoCAD .NET :: How To Force GC To Clear Memory After BindXRef

I have a issu when i use BindXRef. I have 4 XREF in my dwg.  so i use à Do / While for each XREF i have found. It work fine but whrn the Xref is big File, i have the issue "Out Of memory".

So the question : How i can Force the GC to clear all memory not used. My Think is to force the GC to Clear the memory before to use BindXRef() with only one XRef before to BindXRef with another.

Here my code  :

Dim LockDoc As DocumentLock = doc.LockDocument Dim MemNumBoucle As Integer = -1 Dim CollXRef As New ObjectIdCollection Do CollXRef.Clear() Dim xg As XrefGraph = db.GetHostDwgXrefGraph(True) Dim root As GraphNode = xg.RootNode Using tr As Transaction = db.TransactionManager.StartTransaction For o = 0 To root.NumOut - 1 Step 1 Dim child As [Code]......

In this example i cant BindXREf ('R+1') alone. I need to BindXRef('ARCHI') before