How do I remove a key completely from Database

I want to completely remove a vehicle from geoFire, but when I run this:

@Override 
    public void onKeyExited(String key) { 
        // Remove any old marker 
        Marker marker = this.markers.get(key); 
        if (marker != null) { 
            marker.remove(); 
            this.markers.remove(key); 
        } 
    } 

It is removed from the current view, but when I refresh the location, the vehicle is there.