According to articles 8cpv. 1 and 23 LIVA, services performed for customers with registered office or domiciled abroad are VAT exempt, as long as the employment and use happens abroad.
If the place of performance of services isn't on Swiss soil, it is considered performed abroad, and therefore is not subject to tax on services performed in Swiss territory.
The place of employment or use is, for the performance of services called intangible, the place where the customers has his registered office or domicile.
In accordance to art. 3 LIVA it is intended by performance of services, every performance that does not include any supply of goods.

“This document is a simple translation into English of the original document in Italian, the official language of Cantone Ticino, which can be found on the website www.csc-lugano.ch. Therefore, in the event of inaccuracies, errors, imprecisions, or difficulties in interpreting this document, the original document in Italian shall prevail; this also applies if there is a contrast between what is reported in this document and what is reported in the original document in Italian. - Il presente documento è la traduzione semplice in lingua inglese del documento originario in lingua italiana, lingua ufficiale del Cantone Ticino, presente sul sito www.csc-lugano.ch; pertanto in caso di inesattezze, errori, imprecisioni, difficoltà interpretative del presente documento, prevale il documento originario in lingua Italiana; questo anche nel caso in cui vi fosse un contrasto fra quanto riportato nel presente documento e quanto riportato sul documento originario in lingua Italiana.”