Thank you. Just grammatical or grammatical and idiomatic?It would be grammatical without it.
It depends on the situation. In what context would you use "scrubbing at" in that sentence?
I asked you to give us a sentence/context in which you would use "scrubbing at". Your sentence uses only "scrubbing".
Well, for instance, while I was drinking coffee suddenly I spilt some drops on my shirt. I took a cloth and and began to clean my shirt. In that situation,
I stood in the middle of the kitchen and started scrubbing at my shirt with the cloth.
Does it sound natural?
Please tell us where you heard or saw the sentence in question.
Macmillan English Dictionary for Advanced Learners CD-ROM 2nd Edition. CD-ROM © Macmillan Publishers Limited 2007. Text © A&C Black Publishers Ltd 2007.Scrub
He stood there scrubbing at his shirt with the towel.
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