[Google Maps API v2] layer reloading

Hi,
in my script I have a form that contains layer names. When a checkbox
is checked than a function loading data from database runs. Unchecking
a box results in hiding a layer.
But when I check again the old layer and a new one is set on the map.
What shall i do to avoid loading old layer?
clearOverlays results in clearing all layers which I want to avoid.

my function begins as:
function points(){
// here in this moment my old layer in set on the map
GDownloadUrl("points.php", function(dane,kod) {
....//here is my code for data parsing and setting overlay for
each point separatedly on the map
});
}

Can somebody help me?

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