How to calculate only active sheet when using MACRO to highlight selected row

Hello,

I found the below MACRO solution which together with conditional formating highlights the selected row. Works perfectly, only that if multiple workbooks are open it will highlight the same exact row on the active sheet of other open workbooks. Is there a way to "calculate" only the active sheet of active workbook and not all open workbooks?

Private Sub worksheet_selectionchange (ByVal target As Range)
Application.Calculate
End Sub

CF formula: =IF(Cell("row")=row(A1),True,False)

I implemented this solution because my older solution (below) although it works very well, inactivated the "undo" button on my sheets everytime I selected a new cell and I was looking for a workaround that still allowed me to "undo." I like that in the old solution (below) with multiple workbooks open the last highlighted cell on any active sheet remains unchanged (highlighted) when I select the other workbook or any other program, like having a ruler on the screen to indicate the last selected row.

Private Sub Worksheet_SelectionChange (ByVal Target As Range)
If Not Intersect(Target, Range("A11:P1000")) Is Nothing Then
Range("A1").Value = Target.Row
End If

Old CF formula: =$A$1=row()