Ignoring global cooldown

[Benalish]

Greetings,
I've created an icon that lights up when a spell is ready to use. Sometimes though, the icon blinks (disappears for a moment): I think it's a problem due to the global cooldown. I tried to work around this problem like this:

local usable, _ = IsUsableSpell(spellName)
local start, duration = GetSpellCooldown(spellName)
local ignore, gcd = GetSpellCooldown(61304)
if (usable) then
     if (duration == 0 and (start < ignore)) or (duration <= gcd) then --ignore global cooldown
          --show icon
     end
else --hide icon
end

Is there a better method?