Please answer a question about the following article about Tajikistan:

It was temporarily under the control of the Tibetan empire and Chinese from 650–680 and then under the control of the Umayyads in 710. The Samanid Empire, 819 to 999, restored Persian control of the region and enlarged the cities of Samarkand and Bukhara (both cities are today part of Uzbekistan) which became the cultural centers of Iran and the region was known as Khorasan. The Kara-Khanid Khanate conquered Transoxania (which corresponds approximately with modern-day Uzbekistan, Tajikistan, southern Kyrgyzstan and southwest Kazakhstan) and ruled between 999–1211. Their arrival in Transoxania signaled a definitive shift from Iranian to Turkic predominance in Central Asia, but gradually the Kara-khanids became assimilated into the Perso-Arab Muslim culture of the region.

What was the name of the region when it was the cultural center of Iran?
Khorasan