Attention to itching makes me unable to focus on anything else
Here's the canonical answer:

In this way he dwells contemplating feelings in feelings internally,
or dwells contemplating feelings in feelings externally, or dwells
contemplating feelings in feelings [both] internally and externally;
or dwells contemplating in feelings [their] nature of arising, or
dwells contemplating in feelings [their]  nature of vanishing, or
dwells contemplating in feelings [their] nature of [both] arising and
vanishing.  Or else his mindfulness that ‘there are feelings’ is
established simply to the extent necessary for bare knowledge, for
repeated mindfulness. And he dwells independent, and does not cling to
anything in the world. Thus also, monks, a monk dwells contemplating
feelings in feelings. (Satipaṭṭhāna Sutta, MN10 translated by Aggacitta Bhikkhu)

Take note though that feelings here does not refer to the itch, but how you feel about it.