I have a web app that contains 5 listboxes with data that is loaded on page_load. In trying to develop a web app that has increased performance by keeping frequently accessed or expensive data in memory rather than relying on repeated database calls, I've created dataSet caches for each listbox. An example of one of the caches is given below:

     Public Sub LoadDistrictData(ByVal e As String)
      If Cache("Dist") Is Nothing Then
         Dim dsDist As New DataSet
         dsDist = getDistrict()
         Cache.Insert("Dist", dsDist, Nothing, DateTime.Now.AddMinutes(10), Nothing)
      End If

      Dim dvDistrict As New DataView(Cache("Dist").Tables(0))
      lstDistrict.DataSource = dvDistrict
      lstDistrict.DataValueField = "Distrc"
      lstDistrict.DataTextField = "cDistrict" '"DIDSNM"
      lstDistrict.DataBind()
   End Sub

    Function getDistrict() As DataSet
      Dim dsDist As New DataSet
      If Cache("Dist") Is Nothing Then
         Dim daDistrict As New SqlDataAdapter("sp_SelectDistrict2", sqlConnWhere)
         daDistrict.SelectCommand.CommandType = CommandType.StoredProcedure
         Dim workParam2 As SqlParameter = Nothing
         workParam2 = New SqlParameter("@regID", System.Data.SqlDbType.VarChar)
         workParam2.Direction = ParameterDirection.Input
         workParam2.Value = ViewState("Region")
         daDistrict.SelectCommand.Parameters.Add(workParam2 )
         Try
            daDistrict.Fill(dsDist)
         Catch ex As Exception
            lblInfo.Text = "Database error: " & ex.Message
            Exit Function
         End Try
         Cache.Insert("Dist", dsDist, Nothing, DateTime.Now.AddMinutes(10), Nothing)
      End If
      Return Cache("Dist")
   End Function

    Private Sub lstDistrict_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles lstDistrict.SelectedIndexChanged
      Dim x As Integer
      Dim distsel As Integer = 0
      Dim dstval As String
      For x = 0 To lstDistrict.Items.Count - 1
         If lstDistrict.Items(x).Selected = True Then
            dstval = dstval + Convert.ToString(lstDistrict.Items(x).Value)
            distsel = distsel + 1
         End If
      Next
      ViewState("distsel") = distsel
      ViewState("Territory") = dstval
      LoadTerritoryData(ViewState("Territory"))
      ......other subs
   End Sub

Both the data and cache load correctly. However, a selection in one listbox (the first listbox) is suppose to filters data in the remaining 4 listboxes. But since my cache is not equal to NOTHING then the updated ViewState("Region") (created on SelectedIndexChange of the first listbox) is not used as the parameter which will filter the remaining listboxes. Instead the previous Cache is used. I could set the cache equal to NOTHING or Cache.Remove("Dist") on selectedindexchange, but that would require a hit to the server again (which is what I'm trying to avoid). Is there a way to FILTER the EXISTING dataSet Cache? I guess I'm going about this the wrong way. Any help would be greatly appreciated.

Thanks