Scale can be rubbed off with rubbing alcohol. It won't hurt the plant, but the scale will die! I do this all the time on my citrus. Didn't know Sago could be a host for scale.

still would treat the plant with a systemic, even if you remove all the leaves... you can wipe it off, but the leaves will be yellow spotted and look sad from now on until new leaves replace them. And they will eventually.

That won't take care of your problem. If you have the Asian scale, they go dormant in the root system over the winter so you can treat the top all you want, but if you don't treat the root system, you will never get rid of the problem. How bad do the leaves look right now? I would spray the entire above ground plant with horticultural oil and mulch the entire root area with the used coffee grounds that Starbucks gives away for free. These will kill the scales in the roots every time it rains. I would only remove the really bad looking leaves because the plant could use as much energy as possible. I would also give it some fertilizer to give it some energy to fight back. The scales are sucking out all the starch content in your plant and you need to help get the plant up to full strength again.