Using compute shader to return whether texture has certain colour

I'm writing a Compute Shader which I need to do a very simple task: check whether any pixel in the image has green == 1 and blue > 0.5. (For clarity - the green channel is a 2d "light" and the blue channel is that lights "trail" - I want to detect whenever the light crosses back over its trail.)

I'm as far as displaying the overlap (shown in white) for debugging purposes, but I have no idea how to do something as simple as return a value indicating whether the texture actually contains an overlap. My confusion stems from how threads work. I have a float buffer with room for a single float - I simply need a 1 or 0.

For clarification the following two images show a "before" and "after" - all I need is a single "true" value telling me that some white exists in the second image.

The compute shader is as follows:

 #pragma kernel CSMain
 
 Texture2D<float4> InputTexture;
 RWTexture2D<float4> OutputTexture;
 RWStructuredBuffer<float> FloatBuffer;
 
 [numthreads(8,8,1)]
 void CSMain(uint3 id : SV_DispatchThreadID)
 {
     // need to detect any region where g == 1 and blue > 0.5
 
     float green = InputTexture[id.xy].g;
     float blue = round(InputTexture[id.xy].b);
 
     float overlap = round((green + blue) / 2.0);
 
     OutputTexture[id.xy] = float4(overlap, overlap, overlap, 1);
 
     // answer here?? Note that the output texture is only for debugging purposes
     FloatBuffer[0] = ??
 }